<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8">
    <title>设置下边框的颜色</title>
    <style>
        p {
            border-style: solid;
            border-bottom-color: #ff0000;
        }
    </style>
</head>

<body>
    <p>This is some text in a paragraph.</p>
</body>

</html>